1. Field of the Invention
This invention relates to gas measuring devices and methods, and more particularly to exhaust gas static pressure sensing devices and methods.
2. Description of the Related Art
It is desirable in various applications to measure the static pressure of a gas flowing through a housing. Static pressure sensors are common in engine exhaust streams, whether inside the engine or on the engine's aftertreatment system, to determine exhaust gas recirculation fraction, exhaust manifold pressure, or the pressure drop over an exhaust treatment device or backpressure caused by such a device. One such device is a diesel particulate filter, use of which is becoming more prevalent due to increasingly stringent environmental regulations of diesel engine emissions. Accurate static pressure readings are important for proper functioning of engine and aftertreatment system components, as inaccurate readings can result in engine or component failure.
Static pressure is measured by inserting a gas sampling tube into the wall of the housing, pipe, Venturi, or other component through which the exhaust gases are passing, the tube having one end, with an opening, at the wall and the other end operatively attached to a pressure sensor.
It is common to place static pressure sampling tubes upstream and downstream of a diesel particulate filter to determine the state of the filter, i.e., how much soot or other particulate matter has been captured by and is residing in the filter. Too much particulate matter can cause poor engine performance or uncontrolled particulate oxidation on the filter, damaging or destroying the filter and surrounding components.
Exhaust gases generally contain a wide variety of chemical constituents, including soot, hydrocarbons, water, oxides of carbon, and carboxilates, each of which can and often does come out of suspension and form a deposit on an exhaust train component. One of the problems associated with static pressure sampling tubes is the formation of deposits on their openings, skewing the static pressure sensed by the sensor attached to the tube. In the case of sampling tubes associated with diesel particulate filters, this can cause the engine controller to unduly delay regeneration of the filter (a controlled oxidation of the particulate matter on the filter), causing filter damage or failure.